One of my users has a large spreadsheet, but not large enough to cause the problem I will describe.. The user opens the spreadsheet in the Bitrix browser applet and saves it. When they then next open it in Google sheets, they find that they have exceeded the maximum cell count. I *believe* that the problem may be related to this: https://support.microsoft.com/en-us/kb/244435. My guess is that perhaps the Bitrix app is either:

1) storing data like formatting in a hidden cell way outside of used cells2) making some other cell, or filling in whitespace3) both

Such that when opened next in Google docs, Google thinks its too big. He can manually delete all the unused whitespace in the sheet to get around the problem but its a hassle.